Script for Laboratory: Designing embedded ASIPs - CES

3.3.2 Debugging with dlxsim
This chapter assumes, that you are not only used to the assembler code and dlxsim, but that
you are also used to the compiler (Chapter 8.3) and inline assembly (Chapter 8.4).
General Points:
• Compare the results from the CoSy compiled version and the gcc-compiled version. For
the gcc compiled version you have to add printf statements for all essential variables, like:
#ifndef COSY
printf(“temp1: %i\n”, temp1);
#endif
For the CoSy-compiled version, you have to make the essential variables global, for example
moving the variable “temp1” from inside the main method to a global part outside
the main method. All global variables will get an own label in the assembly code with an
underscore before the name, e.g. the variable “temp1” will get the label “_temp1”. In
dlxsim you can see the value of such global variables with the “get” instruction, e.g. “get
_temp1 i”.
Debugging with dlxsim:
• Sometimes the dlxsim simulation aborts with an error message, e.g. when a load
instruction is trying to access an address that is outside the simulated memory range. In
such cases, you first have to find out, which instruction is causing this crash. With the
instruction “get pc” you can see the address which is currently executed. With the instruction
“get {address} i” you can see which instruction is placed at this address and at which
label this instruction can be found. With the instruction “get {Address}-0x10 20i” you can
see the context of this instruction.
• Getting more debugging information from dlxsim is very helpful to understand, what the
assembly code is doing. Therefore, the dlxsim starting parameters “-da#” and “-dbb#” are
useful. You have to replace the “#” with either a “1” to turn the option on or with a “0” to
turn it off.
• da#: Debug Assembly. This option is turned on by default and it will print status information
on the screen for every jump/branch/load/store-instruction. You can print
additional status information by adding your needed information into the sim.c of
dlxsim.
• dbb#: Debug Base Blocks. When you turn on this option then at every start of a baseblock
all changed register values will be printed. A base block is an elementary block
of assembly code that is only executed sequentially. This means, that either all instructions
of a base block are executed (one after the other) or none of them is executed at
all. The borders of a base block (beginning/end) are jumps and labels. The simulation
will create a huge amount of output on the screen if you turn this option on. Therefore
it is recommended, that you copy the output to a text file for easier reading. You can
automatically print everything into a text file if you start dlxsim like:
“../dlxsim -fassembly.dlxsim -dbb1 | tee output.txt”
The “tee” program will copy all output to the screen and to the file.
- 29 -